Apparatus for electrolysis



Oct. 29, 1940. H, L STEWART 2,219,342

APPARATUS FOR ELECTROLYSIS Filed June 26, 1936 2 Sheets-Sheet l 'l IlIlI "lll Oct. 29, 1940. H L STEWART 2,219,342

APPARATUS FOR ELECTROLYSIS Filed June 26, 1936 2 Sheets-Sheet 2 @EBM f8i6 i? Patented Oct. 29, 1940 APPARATUS F B. ELECTBOLYSIS Hubert L.-stewart, Pittsburgh, rs., assigner, by

mesne assignments, to Koppers Gompany, a corporation of DelawareApplication June' 26,

6 Claims.

This invention relates to improvements in apparatus for electrolysis.More particularly, the invention relates to cells employed for theelectrolysis of solutions of materials to generate useful productstherefrom.

In the accompanying drawings which serve to illustrate the presentinvention, and in which like reference characters denote like parts inthe apparatus.

Figure 1 is a sideelevational view of an elec trolyzer having aplurality of cells;

Fig. 2 is a view of one side of a plate used as an electrode inanelectrolyzer comprising the present invention;

Fig. 3. is a vertical sectional view showing the relative positioning oftwo plates to form a cell;

Fig. 4 is an elevational view of a vertical edge of a. plate;

Fig. 5 is a view of one side of a modified form 20 of plate;

Fig. 6 is a sectional view of a plate on line 8 8 of Fig. 5 in thedirection of the arrows;

Fig. 'I is a sectional view of a portion of a plate showing one form ofa structural detail thereof;

Fig. 8 is a view on line 8-8 of Fig. 3 showing the structure of meansprovided between the plates.

Referring to Fig. 1 of the drawings, the appara- 30 tus shown by way ofexample includes a bipolar electrolyzer of the multi-cell, lter-presstype designated generally by the numeral I, means for .introducingliquids into the cells, and means for withdrawing materials therefrom ina particular 35 manner to be described below.

The electrolyzer I comprises a series of metalli plates or electrodes 2clampedtogether in a heavy frame 3, electrically insulated from oneanother and separated by diaphragms 4 (described in 4fur- 0 ther detailbelow) of porous fabric, such as asbestos fabric or canvas. The plates 2are recessed centrally to form a cell between opposing faces, each cellbeing divided by the diaphragm material into an anolyte chamber and a.catholyte cham- 45 ber. In the drawings, the electrolyzer is shown withtwenty-.one intermediate plates each centrally recessed on both sides,and two end plates, the master anode 5 and the master cathode 6, eachcentrally recessed on the inner side only.

The frame 3 may be of any type suitable for clamping the plates tightlyagainst each other. Channel bolting strips 'I may be welded on the outerside of both the master anode 5 and the master cathode 6. Tie bolts 8are provided which 55 are properly insulated from the channels at both193e, serial No. 37,569

(ci. s-25s) ends. For instance, a fiber bushing 9 and a. ber washer IIImay be provided to insulate the ends of the tie bolts 8 from the channelstrips l.

Figs. 2 to 8 inclusive illustrate the construction of the plates orelectrodes 2. Each plate is provided with passag'eways in the bodythereof for conveniently introducing an electrolyte into the cells andfor `withdrawing solutions and gases therefrom. 'I'he plate, shown inFigs. 2, 3 and 4, is an intermediate plate. It is recessed centrally onboth sides, shoulders II and I2 being formed at and around the edges.Passages I3 and Il extend through the shoulders II and I2 respectivelyand communicate with the recess on op posite sides of the plate. Thepassage I3 leads to a passage I5 and the passage Il leads to a passageI6. The passages I5 and I6 extend through the thickness of the plate inspaced projections Il and I8 extending from the upper edge of the saidplate. When a plurality of plates are brought together, the passages I5and I6 coincide with corresponding passages in each plate and form gasoiftakes I5' and I6' through which gases from opposite sides of theplates are withdrawn.

An important feature of the present invention is the provision ofpassages in the plates for the introduction and withdrawal of liquids.As illustrated by way of example, passages I8 and 20 extend into thebody of a plate preferably in the portions of the shoulders II and I2 onthe lower edge of the plate and substantially parallel with said edge.The passages I9 and 20 may extend from either of the normally verticaledges of a plate (Fig. 2), but preferably from the same edge (Fig. 6) tothe opposite edge at which the passages xnay be dead-ended or they mayextend part of the way through as shown. Ports 2| connect the centralrecessed portion on one side of a plate `2 to the passage I9, and ports22 connect the central recessed portion on the other side of the plateto the passage 20.

- In Fig. 3, two plates 24 and 25 similarly constructed are shownassembled to form a cell 26 of an electrolyzer. Passages 21 and 28 nearthe level 29 of the electrolyte extend into each of the plates 24 and 25from either one of the outer edges. In Fig. 2, the passage 2l is shownextending into the electrode from one edge, and the passage 28 is shownextending into the electrode from the opposite edge of a plate.

The passage 2l is connected to the surface of one face 30 of a plate byports 3i. The passage 28 is connected to the surface of the oppositeface 32 of the plate by ports 2l. The face 38 of a Y between the plates.

plate is preferably provided with a nickel plating 34 that serves as theanode. The iron surface of face 32 serves as the cathode of a cell.

lThe diaphragm 4, referred to above, is clamped On either side of thediaphragm, gaskets 36 and 31 are fitted to provide for the properinsulation of the plates from one another and to prevent leakage of theelectrolyte solution. A preferred form of gasket is shown in Fig. 8.This gasket made of rubber, forv example, frames a central portion ofthe diaphragm 4 which is left exposed to the electrolyte. The gasketextends inwardly from the outer edge of a plate and beyond the inneredges of the shoulders II and I2. The upper horizontal portion of agasket extends downwardly from` thetop of a cell to slightly below theliquid level (see Fig. 3) to prevent, by highly effective means, themixing of gases, that is, to keep gas generated at the anode separatefrom the gas generated at the cathode.

'Ihe lower horizontal portion and the vertical-side portions of thegasket prevent current from passing through the diaphragm between theedges of adjacent electrodes. Openings 38 andy 39 in the gasket,register with the passages I5 and I6 respectively in a plate. Insulatingtubular sections 48 and 4I are providedas linings for the passages I5and I6 respectively to prevent any escape of current in case entrainedelectrolyte collectsvin the gas oltakesfl and I6 (Fig. 1).

Nipples 42 are provided at the outlets of each of the passages I9, 20,21 and 28, to which nipples, i'lexible tubular means are removably con!nected. The tubular means are preferably made of insulating materialsuch as rubber. In Fig. 1, the tubular means 43 are shown connecting thepassages 21k of each plate 2 to a manifold `44. Tubular means 45 connectthe passages 28 of each plate 2 to a manifold 46. Tubularmeans 41connect the passages I9 of each plate 2 to a manifold 48. Tubular means49 connect the passages 20 of each plate 2 to a manifold 50. Themanifolds 44, 46, 48, and 59' are each at 5I, 52, 53, and 54respectively.

The manifold pipe 44 is provided with a vertical extension 55 and abranch pipe 56. The manifold pipes 46 and 48 are both connected to avertical pipe 51 provided with a branch pipe 58 extending downwardlyinto'a tank 59. A pipe 60 leads from the tank 59 to a pump 6I. vThe pump6I is connected to the open end 62 of the pipe 51 by means of a pipe 63.

The manifold pipe 50 is connected to a vertical extension 64 providedwith a branch pipe 65( In the modified electrode plate shown in Figs. 5,6 and' 7, instead of a plurality of ports such as 2I, 22, 3I and 33connected to the passages I9, 20, 21 and 28 respectively, slots 66, 61,68 and 69 may be provided for ingress or egress of liquids through thepassages 10, 1I, 12 and 13 respectively. The slots may extend part ofthe way or entirely across the central surfaces of the electrodes andare preferably narrower than the diameter of the passages, therebyforming constricted apertures as shown in Fig. 7.

The electrode plates described above for a filter-press type -ofelectrolyzer make it possi,

ble to introduce electrolyte solution or withdraw products ofelectrolysis or both simultaneously,

in a highly efficient manner. If a product of electrolysis formed ina-cell, has a specific gravity less than that of the electrolyte, theuse of the electrode makes it possible to withdraw the product directlyfrom the upper portion of the surface of the electrode at which theproduct dead-ended is formed while introduction of the electrolyte isaccomplished at a lower level in the cell. Also, if a product ofelectrolysis has a. specific gravity greater than that of theelectrolyte, means are provided in the electrode at whichthe heavierproduct is formed, for introducing electrolyte solution at an upperlevel in a cell at the surface of the electrode while withdrawal of thesaid heavier electrolysisproduct is accomplished at a lowerlevel in thercell. The electrode plate employed makes it possible to withdrawproducts of electrolysis, from zones in a. cell in which they are mostconcentrated.

The tubular connections between the cells and the several manifolds maybe interchangeable to provide-for feeding electrolyte and lwithdrawing4electrolysis products at the desired levels depending upon theirrelative specific gravities. The manifolds 44, 46, 48 and 50 arepreferably spaced some distance from the cell (as much as ve feet insome cases) to prevent, as much as possible, any current flow throughthe liquids in the manifolds. To further prevent any possible loss ofcurrent through the insulating tubular, connections and the manifolds,suitable means may be provided by which, the resistance of theelectrolyte in the tubular` means is increased. For instance theinstallation of overvoltage dams may 4'be provided. Such dams mayconsist of two nickel screen discs placed transversely in the insulatingtubular connections spaced apart and connected by a Wire of lowresistancesuch as iron or copper. The voltage necessary in such aconstruction to overcome the resistance of the electrolyte in the saidtubular connections is increased in amount equal to the hydrogen andoxygen overvoltages on nickel in view of which the ow of current throughthe said connections and manifolds will be decreased. A dam comprisingtwo screen discs d and d' held inspaced relation, and a. connecting wirew is shown in Fig.- 2 in a tubular connection c, a portion of which isenlarged for purposes of illustration.

Avmethod of operating the electrolyzer shown in the accompanyingdrawings may be illustrated in connection with the electrolysis ofcertain chemicals. Sodium carbonate (Na2CO3) solution, for instance, iselectrolyzed to produce sodium hydroxide (NaOH) and sodium bicarbonate(NaHCO).

Sodium carbonate in an aqueous solution containing about 1.8 lbs. sodiumcarbonate per gallon to about 2 lbs. per gallon is pumped from the tank59 by means of the pump 6I into the pipe 51. They solution may, ifdesired, be preheated to about 60 C. to 80 C. by means of a steam coil14 in the tank 59. The level 29 of the electrolyte in the cells ismaintained con-` stant by means of the overow pipe 58 which returnssurplus electrolyte solution toA the tank 59.L The solution entering thepipe 51 flows through the manifold' 46, the flexible tubular.

means 45, the passage 28ports 33 (or passages 1I and slots 61) and intothe upper zone of the cathode chamber of each cell 26. The electrolytealso flows through the manifold 48, the exible tubular means l41', thepassages I9, ports 2| (or passages 12 and slots 68) and into the bottomoftheanode chamber of each cell 26.

Upon flow of current from a generator 15 (diagrammatically shown inFig. 1) sodium bicarbonate is generated at the anode of each cell, andsodium hydroxide is generated at the cathode of each cell.l Thebicarbonate solution generated, having a lower specific gravity than thesodium carbonate solution being electrolyzed, rises in the cells in theanode chambers and is Withdrawn near the level of the electrolyte or asclose 4to the liquid-gas interface as is practicable through ports 3l,passages 21 (or slots 68 and passages l0) exible tubular means 43, andmanifold pipe 44; and overflows through the pipe 56. The generatedsodium hydroxide solution, having a higher specific gravity than thesodium carbonate solution being electrolyzed, is withdrawn from thebottom of the cathode chamber of each cell through ports 22, passages20, (slots 59 and passages 13) flexible tubular means 49, and manifoldpipe 50; andoverfiows through the pipe 65.

As indicated in the drawing, (Fig. 1), the overow pipe 56 is at asilghtly lower level than the overow pipe 58, and the overflow pipe isat a slightly lower level than either pipes 56 or 58. By means of thisarrangement a difference of the static heads of the various solutions ismaintained depending upon the specific gravities thereof. The levels atwhich the electrolysis products are withdrawn will depend upon theirrelative specific gravities. For thispurpose, pipes 55 and 64 may beconstructed so as to be extensible. Alternatively, a swivel pipeconnection 85 such as that shown connected to the pipe 65 may beprovided which may be turned any angle. 'I'he pipe 85 is shown in fullline in a position at which the liquid is withdrawn at the level of thepipe 65. Sodium bicarbonate solution preferably has a hydrostatic headgreater than that of the caustic soda in order to prevent infiltrationof caustic soda from the cathode chamber into the anode chamber. Suchinfiltration tends to neutralize the eil'ects of electrolysis.

A substantial space between the level of the electrolyte and the tops ofthe cell chambers is preferred so that no liquid is carried with eitherthe hydrogen or oxygen through the passages I3 or I4 respectively.

As indicated above, the electrode plates are bipolar, nickel platingbeing provided on the anode side and iron on the cathode side. Stainlesssteel containing 18% chromium and 8% nickel may be used in the anode, ifdesired. Copper, cadmium, or Monel metal may be substituted for the ironas the cathode. Iron for the cathode is preferred because of its lowover-voltage. One or more leads are attached to the master plates. Morethan one lead to each of the said plates is used to provide for properdistribution of current.

The cell temperature and current density are maintained fairly constantby regulating the voltage. A cell or electrolyzer may be operated with acurrent density of about 50 amperes per squarev foot to about amperesper squarefoot. The cell temperature rangesy preferably from about 60 C.to about 80 C. 'Ihe temperature should not be so high as to produce tooviolent an evolution of gases and should not be so low as to raise theresistance of electrolyte too high. The use of the form of plateprovided with passages described above is advantageous in that itpreheats the electrolyte as the solution flows through the passages. v

The rate of introduction of sodium carbonate solution into the cellsdepends on the concentration of solutions that are to be withdrawn. Thefeed to the cathode chambers may differ, if desired, from the feed tothe anode chambers. In the electrolysis of the sodium carbonatesolution, the feed to the cathode chamber may be about 1.0 gallon perhour per kilowatt hour and to the anode chamber about 1.2 gallons perhour per kilowatt hour. For the purpose of thus controlling the feed,,valves 80 and 8| may be provided in pipes 48 and 48 respectively. Afeed of approximately twenty per cent faster through the anode chamberis found advantageous in preventing the accumulation 0f solid sodiumbicarbonate. The cell feed is preferably at such a rate as to convertfrom about 40% to about 48% of the sodium present as sodium carbonateinto sodium hydroxide, and from about 40% to about 48% of the sodiumpresent as sodium carbonate into sodium bicarbonate leaving sodiumcarbonate unchanged to the extent of about from 4% to 20%.

Throughout the operation of a cell the cell feed-current density ratiois controlled in such a manner as to give maximum yields of electrolysisproducts. Periodical analyses of the electrolysis products may be madefrom time to time to determine the concentrations of sodium Ahydroxideand sodium bicarbonate.

In the commercial operation of the cell, a current eiliciency of between92 and 98% and an energy efliciency of between 46 and 52% areobtainable. The yields of 0.71l to 0.79 pound of sodium hydroxide perkilowatt hour can be obtained.

Besides electrolyzing sodium carbonate the process may be applied tosolutions of potassium carbonate, and of borax. Borax will producesodium hydroxide and boric acid. Potassium carbonate will be convertedinto potassium hydroxide and bicarbonate. Disodium phosphate isconverted into sodium hydroxide and monosodium phosphate.

It is apparent from the above description that various changes maiy bemade in the form, construction and arrangement of parts withoutdeparting from the spirit and scope of the invention or sacrificing allof its material advantages, the forms hereinbefore cited by way ofillustration being merely the preferred embodiments thereof.`

What I claim is:

1. In apparatus for electrolysis, comprising a generator of thefilter-press type having a plurality of electrode plates clampedtogether face to face and centrally recessed to provide a cell betweeneach pair of plates; manifold means, and connecting means constructed ofinsulating material between each -of the cells and the said manifoldmeans for the passage of solution to Aor from the cells,` and anovervoltage dam in each of the said connecting means, the said damcomprising spaced screens positioned transversely in the said connectingmeans, and a wire of low resistance connecting the said screens.

2. In apparatus for electrolysis comprising a plurality of cells whichcells connect-with each other by passage means for conducting liquid toor from the said cells, the said passage means having a wall constructedof insulating material, an overvoltage dam in such passage means, thesaid dam comprising spaced metallic, foraminate means positionedtransversely in the said passage means, and an electrical conductor oflow resistance connecting the said spaced foraminate means.

3. Apparatus comprising means for inhibiting the flow of current througha passage having a wall constructed of insulating material andcontaining an electrolyte, the s'aid means comprising spaced metallic,foraminate means positioned transversely in the said passage, and anelectrical conductor of low resistance connecting the said foraminatemeans.

4. In apparatus for electrolysis, a solid electrode plate for a bipolarelectrolyzer of the multicell, iilter press type, having separateanolyte and catholyte chambers and a separate gas oitake for eachchamber, a plurality of unconnected passages of relatively small crosssection in said plate l@ each extending from an outer edge of the plateinto the body thereof to a working face of the plate, one of saidpassages extending to the surface of the plate at points extendingacross a workingface of the plate adjacent butl below the 15 normallevel of electrolyte solution in the electrolyzer, and another of saidpassages extending to the surface of the plate at points extendingacross a working face of the plate adjacent the lower edge of theworking face of the plate, each g@ of the said passages servingalternatively for the introduction of electrolyte solution or for thewithdrawal of a. solution of a product of electrolysis at the saidlevels.

5. In apparatus for electroylsis, a solid elec'- 25 trode plate for abipolar electrolyzer of the multicell, lter press type, having separateanalyte and catholyte chambers and a separate. gas oitake for eachchamber, a plurality of unconnected passages of relatively small crosssection in said plate a@ each extending from an outer edge of the plateinto the body thereof to a Y,Working :face of the plate, one of saidpassages extending to the surface of the plate at points extendingacross one Y working `face of the plate adjacent but below the 35 normallevel of electrolyte solution in the electrolyzer, another of saidpassages extending to.

the surface o1' the plate at points extending across the said oneworking face of the plate adjacent the lower edge of the said face, athird of said passages extending to'the surface of the plate at pointsextending across the opposite Working face 5 of the plate adjacent thelevel of the said rstnamed points, and a fourth of said passagese'xtending to the surface of the plate at points extending across thesaid opposite working face of the plate adjacent the level of the saidsecondnamed points, each nof the said passages serving alternatively forthe introduction of electrolyte solution or for the withdrawal of asolution of a product of electrolysis at the said levels.

6. In apparatus for electrolysis, a solid electrode plate for a bipolarelectrolyzer of the multicell, iilter press type having separate anolyteand catholyte chambers and a. separate gas 01T- take for each chamber, aplurality of unconnected passages of relatively small cross section insaid plate each extending from an outer edge of the plate into the bodythereof, a plurality of elongated slots extending substantiallycompletely across a working face ofthe plate, one of said passagesextending to a slot in the working 'face 25 of the plate adjacent butbelow the normal level of electrolyte solution in the electrolyzer, andanother of said passages extending to a slot adjacent the lower edge ofthe Working face of the plate, a portion of each of the said passagesadjacent the said slots tapering toward the latter and each of the said\passages serving altertively for the introduction of electrolytesolution or i'or the withdrawal -of a solution of a product ofelectrolysis at the said levels. l 35 HUBERT L. STEWART.

